High performance refrigerator having evaporator outside cabinet

ABSTRACT

A high performance refrigerator includes a cabinet with a refrigerated interior, a refrigeration fluid circuit having an evaporator located within an insulated evaporator compartment outside the cabinet, and at least one damper that opens to permit air circulation from the refrigerated interior through the evaporator compartment. The refrigerator also includes a eutectic member configured to melt at an operating temperature of the refrigerator. The evaporator cools the refrigerated interior to a temperature below the operating temperature so that the eutectic member melts to cool the refrigerated interior or the evaporator compartment during a defrost cycle. The insulated evaporator cover limits heat transfer into the refrigerated interior during the defrost cycle to avoid temperature spikes in the refrigerated interior.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the priority benefit of U.S. ProvisionalPatent Application No. 61/548,807 (pending), filed Oct. 19, 2011, thedisclosure of which is hereby incorporated by reference in its entiretyherein.

FIELD OF THE INVENTION

The present invention relates generally to refrigerators or freezersand, more particularly, to refrigeration systems for use with highperformance blood bank refrigerators or plasma freezers.

BACKGROUND OF THE INVENTION

Refrigeration systems are known for use with laboratory refrigeratorsand freezers of the type known as “high performance refrigerators,”which are used to cool their interior storage spaces to relative lowtemperatures such as about −30° C. or lower, for example. These highperformance refrigerators are used to store blood and/or plasma, in oneexample.

Known refrigeration systems of this type include a single loopcirculating a refrigerant. The system transfers energy (i.e., heat) fromthe refrigerant to the surrounding environment through a condenser, andthe system transfers heat energy to the refrigerant from the cooledspace (e.g., a cabinet interior) through an evaporator. The refrigerantis selected to vaporize and condense at a selected temperature close tothe desired temperature for the cooled space, such that therefrigeration system can maintain the cooled space near that selectedtemperature during operation.

One common problem with known refrigeration systems is that theevaporator includes coils that tend to produce and accumulate frostalong the outer surface if any moisture is ambient within the cooledspace. If enough frost accumulation occurs, the ability of theevaporator to remove heat from the cooled space is detrimentallyimpacted. Consequently, known refrigeration systems require a defrostcycle where the evaporator coils are heated to remove the frost. Thisdefrost cycle may be a manual defrost or an automatic defrost, but bothtypes of defrost cycles are undesirable for various reasons.

In a manual defrost cycle, all of the products stored in the cabinet areremoved and the cooled space is left exposed to the ambient environmentto heat up the evaporator coils and melt the frost. This cycle isundesirable because the products stored in the cabinet need to be storedin an alternative refrigerator for the duration of the defrost cycle,and also because the melting process can produce a significant amount ofmoisture that needs to be removed from the cabinet. In an automaticdefrost cycle, the evaporator coils are rapidly heated by a localheating unit or hot gas flow to remove the frost, which is collected bya trough and delivered out of the cooled space. The cooled spacenecessarily undergoes a temperature spike during this automatic defrostcycle, which can jeopardize the products stored in the cabinet.

There is a need, therefore, for a refrigerator that substantiallyminimizes or eliminates a temperature spike within the cooled spaceduring a defrost cycle.

SUMMARY OF THE INVENTION

In one embodiment, a refrigerator includes a cabinet with a refrigeratedinterior and a refrigeration fluid circuit for circulating arefrigerant. The refrigeration fluid circuit includes a compressor, acondenser, an expansion device, and an evaporator located within aninsulated evaporator compartment outside the cabinet. The evaporatorincludes an evaporator coil and an evaporator fan producing air flowthrough the evaporator coil. The refrigerator includes at least onedamper which opens to permit air circulation from the refrigeratedinterior through the evaporator compartment. The refrigerator alsoincludes a eutectic member that melts at an operating temperature of therefrigerator. The evaporator cools the refrigerated interior to atemperature below the operating temperature such that when the at leastone damper is closed for a defrost cycle, the eutectic member melts tocool at least one of the refrigerated interior and the evaporatorcompartment.

In one aspect, the eutectic member is mounted along one of the sidewalls of the cabinet or along the top wall of the cabinet. The at leastone damper is also formed in the top wall such that the eutectic memberacts as a temperature ballast as well as a cold generation device. Inanother aspect, the eutectic member is mounted within the evaporatorcompartment such that the eutectic member melts to cool the evaporatorcompartment during operation of a defrost heater within the evaporatorcompartment.

In another embodiment, a refrigerator includes a cabinet with arefrigerated interior and a refrigeration fluid circuit for circulatinga refrigerant. The refrigeration fluid circuit includes a compressor, acondenser, an expansion device, and an evaporator located within aninsulated evaporator compartment outside the cabinet. The evaporatorincludes an evaporator coil, an evaporator fan producing air flowthrough the evaporator coil, and a defrost heater. The refrigeratorincludes at least one damper which opens to permit air circulation fromthe refrigerated interior through the evaporator compartment. Therefrigerator also includes a controller operable to command therefrigerator to perform a series of steps defining a defrost cycle whenthe evaporator coil requires defrosting. The series of steps includesstopping operation of the compressor and the evaporator fan, closing theat least one damper to thermally isolate the evaporator compartment fromthe refrigerated interior, and starting operation of the defrost heater.The refrigerated interior remains thermally isolated from the evaporatorduring operation of the defrost heater.

In one aspect, the refrigerator also includes a temperature sensor fordetecting the temperature of the evaporator. The controller operatesduring defrosting as follows: when the temperature sensor detects thatthe evaporator has reached a first target temperature above the freezingpoint of water, the defrost heater stops and any remaining moisture isallowed to drip off the evaporator coil. After any remaining moisturedrips off the evaporator coil, the compressor starts. When thetemperature sensor detects that the evaporator has reached a secondtarget temperature below the freezing point of water, the at least onedamper opens and the evaporator fan starts. In one example, the firsttarget temperature is about 10° C. and the second target temperature isabout −25° C. The controller may also be operable to perform the defrostcycle steps as an adaptive defrost cycle, which includes varying timeperiods between defrost cycles and varying lengths of defrost cyclesdependent upon multiple operating parameters.

In yet another embodiment of the invention, a refrigerator includes acabinet with a refrigerated interior and a refrigeration fluid circuitfor circulating a refrigerant. The refrigeration fluid circuit includesa compressor, a condenser, an expansion device, and an evaporatorlocated within an insulated evaporator compartment outside the cabinet.The evaporator includes an evaporator coil and an evaporator fanproducing air flow through the evaporator coil. The refrigeratorincludes at least one valve which opens to permit air circulation fromthe refrigerated interior through the evaporator compartment. Thecabinet includes a top wall adjacent the evaporator compartment, a door,a rear wall, and side walls (including a rear wall) extending betweenthe rear wall and the door. The rear wall includes an inlet duct incommunication with the evaporator and a plurality of inlet ports leadinginto the refrigerated interior. The side walls include an outlet duct incommunication with the evaporator and a plurality of outlet portsleading from the refrigerated interior. The at least one valve controlsflow between the evaporator and the refrigerated interior via the inletduct and the outlet ducts.

In another embodiment of the invention, a method of operating arefrigerator is provided, the refrigerator including a cabinet with arefrigerated interior and a refrigeration fluid circuit including acompressor, a condenser, and an evaporator located in an insulatedevaporator cover outside the cabinet. The evaporator includes anevaporator fan and a defrost heater. The refrigerator also includes atleast one damper separating the evaporator compartment from therefrigerated interior. The method includes stopping operation of thecompressor and an evaporator fan. The at least one damper closes tothermally isolate the evaporator compartment from the refrigeratedinterior. A defrost heater starts operation to remove moisture fromevaporator. The refrigerated interior remains thermally isolated fromthe evaporator during operation of the defrost heater.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description of the embodiments given below, serve toexplain the principles of the invention.

FIG. 1 is a perspective view of a refrigerator including an evaporatorlocated outside the cabinet according to an exemplary embodiment.

FIG. 2 is a schematic representation of the refrigeration fluid circuitused with the refrigerator of FIG. 1.

FIG. 3 is a perspective view of the insulating evaporator cover (shownin phantom) and dampers used with the refrigerator of FIG. 1.

FIG. 4 is a perspective view of an evaporator used with the refrigeratorof FIG. 1, with some of the side panels shown in phantom to revealinterior elements.

FIG. 5 is a cross-sectional side view of the refrigerator of FIG. 1along line 5-5, with the dampers in a closed position and eutecticplates located in the evaporator compartment and the cabinet.

FIG. 6 is a cross-sectional side view of the refrigerator of FIG. 5,with the dampers in an open position.

FIG. 7 is a cross-sectional side view of another embodiment of arefrigerator including an evaporator located outside the cabinet and airducts through the walls of the cabinet.

FIG. 8 is a cross-sectional front view of the refrigerator of FIG. 7.

FIG. 9 is a schematic diagram of the controller and damper or valvedrive elements used with the refrigerators of FIGS. 1 and 7.

FIG. 10 is a schematic flowchart illustrating an operational sequence ofa controller associated with the refrigerators of FIGS. 1 and 7.

DETAILED DESCRIPTION

With reference to the figures, and more specifically to FIG. 1, anexemplary high performance refrigerator 10 according to one embodimentof the present invention is illustrated. Although the terms “highperformance refrigerator” and “refrigerator” are used throughout thespecification, it will be understood that the invention encompasses anytype of cooling device, including a refrigerator comprising a freezer.The refrigerator of FIG. 1 includes a cabinet 12 for storing items thatrequire cooling to temperatures of about −30° C. or lower, for example.The cabinet 12 includes a cabinet housing 14 defining a generallyrectangular cross-section and a door 16 providing access into aninterior 18 of the cabinet 12. The cabinet 12 supports one or morecomponents that jointly define a single-stage refrigeration fluidcircuit 20 (FIG. 2) that thermally interacts with the air within thecabinet 12 to cool the interior 18 thereof. In this regard, therefrigeration fluid circuit 20 described in further detail belowinteracts with warmed air in the interior 18 and cools this air tomaintain a desired cold temperature in the cabinet 12. The refrigerator10 also includes an upper compartment 21 disposed above the cabinet 12and configured to contain the components of the refrigeration fluidcircuit 20 as described in further detail below.

With reference to FIG. 2, details of the exemplary refrigeration fluidcircuit 20 are illustrated. The refrigeration fluid circuit 20 includes,in sequence, a compressor 22, a condenser 24, a filter/dryer 26, anexpansion device 28, an evaporator 30, and a suction/accumulator 32.Each of these elements of the refrigeration fluid circuit 20 is coupledby piping or tubing 34 configured to circulate the refrigerant 36passing through the refrigeration fluid circuit 20. A plurality ofsensors S₁ through S₅ are arranged to sense different conditions of thefluid circuit 20 and/or properties of the refrigerant (shown by arrows36) at various locations within the fluid circuit 20. Each of thesesensors S₁ through S₅ is operatively coupled to a controller 50accessible through a controller interface 52, which permits controllingof the operation of the fluid circuit 20. It will be appreciated thatmore or fewer sensors may be provided than the number shown in theexemplary embodiment of the fluid circuit 20.

The refrigeration fluid circuit 20 is configured to circulate therefrigerant 36 between the condenser 24 and the evaporator 30. Generallyspeaking, heat energy in the refrigerant 36 is transferred to ambientair outside the cabinet 12 at the condenser 24. Heat energy is removedfrom the interior 18 of the cabinet 12 and transferred to therefrigerant 36 at the evaporator 30. Thus, circulating the refrigerant36 through the fluid circuit 20 continuously removes heat energy fromthe interior 18 to maintain a desired internal temperature, such as, forexample −30° C.

The refrigerant 36 enters the compressor 22 in a vaporized state and iscompressed to a higher pressure and higher temperature gas in thecompressor 22. The fluid circuit 20 of this exemplary embodiment alsoincludes an oil loop 54 for lubricating the compressor 22. Specifically,the oil loop 54 includes an oil separator 56 in fluid communication withpiping 34 downstream of the compressor 22 and an oil return line 58directing oil back into the compressor 22. It will be understood thatthe oil loop 54 may be omitted in some embodiments of the fluid circuit20.

Upon leaving the compressor 22, the vaporized refrigerant 36 travels tothe condenser 24. A fan 60 controlled by the control interface 52directs ambient air across the condenser 24 and through a filter 62 soas to facilitate the transfer of heat from the refrigerant 36 to thesurrounding environment. The air flow through the condenser 24 is shownby arrows in FIG. 2. The refrigerant 36 condenses within the condenser24 as a result of this heat transfer. The liquid-phase refrigerant thenpasses through the filter/dryer 26 and into the expansion device 28. Inthis embodiment, the expansion device 28 is in the form of a capillarytube, although it is contemplated that it could instead take anotherform such as, and without limitation, an expansion valve (not shown).The expansion device 28 causes a pressure drop in the refrigerant 36immediately before the refrigerant 36 enters the evaporator 30.

In the evaporator 30, the refrigerant 36 receives heat from the interior18 through a plurality of evaporator coils (not shown in FIG. 2). Anevaporator fan 64 controlled by the control interface 52 forces air flowfrom the interior 18 of the cabinet 12 through the evaporator coils whenfirst and second dampers 66, 68 are opened. The first and second dampers66, 68 are also controlled by the control interface 52. The control ofthe first and second dampers 66, 68 is further described with referenceto FIGS. 9 and 10, below. By virtue of the lowered pressure and the heattransfer from the cabinet 12, the refrigerant 36 vaporizes within theevaporator 30. The vaporized refrigerant 36 is then directed to thesuction/accumulator device 32. The suction/accumulator 32 passes therefrigerant 36 in gaseous form to the compressor 22, while alsoaccumulating excessive amounts of the refrigerant 36 in liquid form andfeeding it to the compressor 22 at a controlled rate.

The refrigerant 36 used in the refrigeration fluid circuit 20 may bechosen based on several factors, including the expected operatingtemperature within the cabinet 12 and the boiling point and othercharacteristics of the refrigerant 36. For example, in refrigeratorswith an expected cabinet temperature of about −30° C., an exemplaryrefrigerant 36 suitable for the presently described embodiment includesrefrigerants commercially available under the respective designationsR404A. Moreover, in specific embodiments, the refrigerant 36 may becombined with an oil to facilitate lubrication of the compressor 22. Forexample, and without limitation, the refrigerant 36 may be combined withMobil EAL Arctic 32 oil. It will be understood that the precisearrangement of the components illustrated in the figures is intended tobe merely exemplary rather than limiting.

With reference to FIGS. 3-6 and in particular FIG. 3, the refrigerator10 includes an insulated cover 70 located outside the cabinet 18 andinside the upper compartment 21. The insulated cover 70 encloses aninsulated evaporator compartment 72 which is isolated from arefrigerated portion 74 within the interior 18 of the cabinet 12. Therefrigerated portion 74 is defined by a top wall 76, side walls 78(including a rear wall 78a and side walls 78b), and a bottom wall 80collectively forming the cabinet housing 14. The insulated cover 70 iscoupled to the top wall 76 of the cabinet housing 14 such that the firstand second dampers 66, 68 open flow into the refrigerated interior 18.More particularly, the insulated cover 70 is coupled to the top wall 76of the cabinet housing 14 to thermally isolate the evaporatorcompartment 72 from the heat energy within the interior 18 as that heatenergy rises within the interior 18 of the cabinet 12. The insulatedcover 70 of the illustrated embodiment is a rectilinear box-shapedmember including a plurality of vertical panel portions 82 extendingbetween two horizontal panel portions 84, one of which is locatedadjacent to the top wall 76 of the cabinet housing 14. The verticalpanel portions 82 and the horizontal panel portions 84 are formed fromone or more thermally insulating panels, such as the hollow vacuuminsulated panel 86 shown in FIG. 3. It will be understood that othertypes of insulating panels may be used in other embodiments of theinvention, including but not limited to foam-based panels.

As shown in FIG. 3, the evaporator 30 mounts into a divider panel 88located generally centrally within the evaporator compartment 72 so asto divide the evaporator compartment 72 into an inlet side 90 and anoutlet side 92. The divider panel 88 is another vacuum insulated panelor foam-based insulated panel in this embodiment, although it will beunderstood that other types of dividing panels may also be used in otherembodiments. The bottom-side horizontal panel portion 82 of theinsulated cover 70 includes an inlet aperture 94 on the inlet side 90 ofthe divider panel 88 and an outlet aperture 96 on the outlet side 92 ofthe divider panel 88. The first damper 66 includes an insulated panelthat is operable to rotate to open or close flow through the inletaperture 94 between the inlet side 90 and the refrigerated interior 18of the cabinet 12. Similarly, the second damper 68 includes an insulatedpanel that is operable to rotate to open or close flow through theoutlet aperture 96 between the outlet side 92 and the refrigeratedinterior 18 of the cabinet 12. Thus, the first and second dampers 66, 68may be operated to enable flow through the evaporator 30.

Also shown in FIG. 3, the first and second dampers 66, 68 areoperatively connected to a damper drive mechanism 100 such as respectivefirst and second servo motors 102, 104 and first and second drive shafts106, 108. The control and operation of the damper drive mechanism 100 isfurther described in detail with reference to FIG. 9 below. It will beunderstood that the first and second drive shafts 106, 108 may beconnected by a conventional drive linkage (not shown) in someembodiments so that only a single servo motor would be required to openand close the first and second dampers 66, 68. In this regard, the firstand second dampers 66, 68 are typically opened (or closed)simultaneously so that flow is enabled through the evaporatorcompartment 72 and the evaporator 30.

Turning to FIG. 4, the evaporator 30 is shown in further detail. To thisend, the evaporator 30 includes an evaporator housing 110 enclosing anevaporator coil 112 extending in a serpentine manner across a width ofthe evaporator 30. The evaporator coil 112 is operatively connected tothe piping 34 of the refrigeration fluid circuit 20, which carriesliquid-phase refrigerant to the evaporator coil 112 and removesvaporized and any remaining liquid-phase refrigerant from the evaporatorcoil 112. The evaporator fan 64 is mounted along the evaporator housing110 at the inlet side 90 of the evaporator compartment 72 so as toactuate air flow through the evaporator housing 110 and through theevaporator coil 112. After flowing through the evaporator coil 112,cooled air exits the evaporator housing 110 and enters the outlet side92 of the evaporator compartment 72.

The evaporator 30 also includes a defrost heater 114 for removing frostbuild up on the evaporator coil 112 as needed or on a regular basis. Thedefrost heater 114 is shown mounted adjacent to the evaporator coil 112in FIGS. 4 and 5, but it will be appreciated that the defrost heater 114may be mounted anywhere within the evaporator housing 110. The defrostheater 114 is operated by the controller 50 and the control interface 52previously described with reference to FIG. 2 to heat up the evaporatorcoil 112 and melt any frost. The evaporator housing 110 further includesa drip pan 116 located below the evaporator coil 112 and configured tocollect and dispose of melted frost to a location outside therefrigerator 10. In this regard, the drip pan 116 is generally angledfrom a horizontal orientation so that moisture dripping from theevaporator coil 112 automatically flows to a moisture outlet (notshown).

With reference to FIGS. 5 and 6, the placement of the evaporator 30within the evaporator compartment 72 outside the cabinet 12 is furthershown. The upper compartment 21 contains the evaporator compartment 72and elements of the refrigeration fluid circuit 20 other than theevaporator 30 (e.g., the compressor 22, the condenser 24, etc.), therebyremoving most of the space-using or heat generating components from theinterior 18 of the cabinet 12. These other elements located within theupper compartment 21 are not shown in FIGS. 5 and 6, although they areschematically shown in FIG. 2. The piping 34 for the refrigerant 36extends through the top side horizontal panel portion 82 of theinsulated cover 70 to deliver refrigerant 36 between the components inthe upper compartment 21 and the evaporator 30 in the evaporatorcompartment 72.

FIGS. 5 and 6 also illustrate two operating states for the refrigerator10. More particularly, in FIG. 5 the first and second dampers 66, 68 areclosed, which thermally isolates the evaporator compartment 72 from therefrigerated portion 74. The evaporator fan 64 is generally inactivewhen the first and second dampers 66, 68 are closed because air cannotbe circulated into and out of the evaporator compartment 72. The defrostheater 114 is only operated in this operational state of therefrigerator 10 so that substantially all of the heat energy generatedby the defrost heater 114 remains within the evaporator compartment 72during a defrost cycle or process. To this end, the temperature spikewithin the refrigerated portion 74 of the interior 18 is reduced oreliminated during the defrost cycle. In contrast, the first and seconddampers 66, 68 are open in FIG. 6 so that air from the refrigeratedportion 74 may flow through the evaporator 30 and the evaporator coil112 for cooling. The air flow actuated by the evaporator fan 64 isschematically shown in FIG. 6 by arrows 120. Thus, relatively warm airenters the evaporator compartment 72 through the inlet aperture 94 andrelatively cold air exits the evaporator compartment 72 through theoutlet aperture 96 in this operating state of the refrigerator 10.

The refrigerator 10 also includes one or more eutectic members 122 asshown in FIGS. 5 and 6. The eutectic members 122 are eutectic plates 122mounted in close proximity to the insulated cover 70. The eutectic plate122 is configured to melt at a predetermined operating temperature basedon the material forming the eutectic plate 122. In this regard, theeutectic plate 122 may be configured to melt around the intendedoperating temperature of the refrigerator, such as −30° C. Thus, theevaporator 30 operates to cool the interior 18 of the cabinet 12 belowthe operating temperature such that the eutectic plate 122 is maintainedin a solid state during normal operation of the refrigerator 10. When adefrost cycle is initiated, the dampers 66, 68 close and the defrostheater 114 begins warming the evaporator compartment 72. The insulatedcover 70 helps prevent the heat energy generated by the defrost heater114 from entering the refrigerated interior 18, thereby reducing anytemperature spike encountered by the interior 18 during the defrostcycle.

The eutectic plate 122 may be mounted along the side walls 78 or the topwall 76 within the cabinet 12. In these embodiments, any heat energythat enters the interior 18 or is generated within the interior 18 iscounteracted by the melting of the eutectic plate 122, which acts as asupplemental cooling device during the defrost cycle. To this end, theeutectic plate also limits the temperature spike within the cabinet 12.When the eutectic plate 122 is located along the top wall 76 of thecabinet housing 14, the eutectic plate 122 may operate as a temperatureballast or additional insulation between the refrigerated interior 18and the evaporator compartment 72.

In another embodiment, the eutectic plate 122 may alternatively bemounted within the evaporator compartment 72. Similar to the previousembodiment, the eutectic plate 122 melts to counteract the detrimentalheating effects of the defrost heater 114. In this regard, the defrostheater 114 heats the evaporator coil 112 to melt frost from theevaporator coil 112 but the heat energy fills the remainder of theevaporator compartment 72 where the heat energy is unnecessary. Once thedefrost cycle is completed, the melting of the eutectic plate 122assists the refrigerant 36 flowing through the evaporator coil 112 tomore rapidly cool the evaporator compartment 72 back to the intendedoperating temperature of the refrigerator 10. Consequently, the eutecticplate 122 may reduce any temperature spike encountered within thecabinet 12 during a defrost cycle or may reduce the overall length of adefrost cycle by more rapidly cooling the evaporator compartment 72 atthe end of such a defrost cycle.

An alternative embodiment of the refrigerator 130 is shown in FIGS. 7and 8. The refrigerator 130 of this embodiment includes many of the samecomponents of the previously-described refrigerator 10, and theseelements are indicated by the same reference numbers in FIGS. 7 and 8.The primary difference of this embodiment of the refrigerator 130 isthat the dampers 66, 68 have been replaced by an air duct and valveassembly. To this end, the evaporator compartment 72 includes an outletvalve 132 for air flow as shown in FIG. 7. The outlet valve 132communicates with an inlet or supply duct 134 extending along the lengthof the rear wall 78a of the cabinet housing 14. The inlet or supply duct134 includes a plurality of inlet ports 136 for delivering chilled airflow (indicated by arrows 138) into all levels of the refrigeratedinterior 18 of the cabinet 12. In contrast to the first embodiment, thechilled air flow enters the cabinet 12 along the entire height of thecabinet 12.

In a similar manner, each of the side walls 78b extending between therear wall 78a and the door 16 includes an outlet or return duct 140 witha plurality of outlet ports 142 disposed along the length of the sidewalls 78b. To this end, a return flow of warmed air (indicated by arrows144) flows from the interior 18 through the outlet ports 142 and theoutlet or return ducts 140 to inlet valves 146 at the insulated cover70. Thus, the inlet valves 146 and the outlet valve 132 control air flowthrough the evaporator 30 via the inlet duct 134 and the outlet ducts140. Because the inlet duct 134 and the outlet ducts 140 extend from thetop wall 76 to the bottom wall 80 of the cabinet housing 14, the airduct and valve assembly of this embodiment of the refrigerator 130enable more thorough air flow through the cabinet 12.

FIG. 9 schematically illustrates the control and actuation mechanismsfor the first and second dampers 66, 68 (or the valves 132, 146). Morespecifically, the first and second dampers 66, 68 are connected to thedamper/valve drive mechanism 100, which is coupled to the controller 50.As understood in the art, the controller 50 may include at least onecentral processing unit (“CPU”) coupled to a memory. Each CPU istypically implemented in hardware using circuit logic disposed on one ormore physical integrated circuit devices or chips. Each CPU may be oneor more microprocessors, micro-controllers, field programmable gatearrays, or ASICs, while memory may include random access memory (RAM),dynamic random access memory (DRAM), static random access memory (SRAM),flash memory, and/or another digital storage medium, and also typicallyimplemented using circuit logic disposed on one or more physicalintegrated circuit devices, or chips. As such, memory may be consideredto include memory storage physically located elsewhere in therefrigerator 10, e.g., any cache memory in the at least one CPU, as wellas any storage capacity used as a virtual memory, e.g., as stored on amass storage device such as a hard disk drive, another computing system,a network storage device (e.g., a tape drive), or another network devicecoupled to the controller 50 through at least one network interface byway of at least one network. The computing system, in specificembodiments, is a computer, computer system, computing device, server,disk array, or programmable device such as a multi-user computer, asingle-user computer, a handheld computing device, a networked device(including a computer in a cluster configuration), a mobiletelecommunications device, a video game console (or other gamingsystem), etc. The controller 50 includes at least one serial interfaceto communicate serially with an external device, such as thedamper/valve drive mechanism 100, for example. Thus, the controller 50functions to actuate operation of the damper/valve drive mechanism 100.

As previously described with reference to the refrigerator 10 of FIG. 1,the damper drive mechanism 100 may be one or more servo motors 102, 104connected to the first and second dampers 66, 68 via corresponding driveshafts 106, 108. However, the damper drive mechanism 100 may includeother types of actuation mechanisms and devices in other embodiments.For example, the damper drive mechanism 100 may be hydraulically driven,pneumatically driven, or mechanically driven such as by various types ofmotors. The damper drive mechanism 100 may be configured to rotate thedampers 66, 68 between open and closed positions as shown in theillustrated embodiment, but it will be understood that the damper drivemechanism 100 may alternatively slide or otherwise move the dampers 66,68 in non-rotational manners as well. Similarly, a valve drive mechanism100 for the refrigerator 130 of FIG. 7 may also include various types ofactuators as readily understood.

An exemplary operation of the refrigerator 10 (or 130) is shownschematically in the flowchart of FIG. 10. In this regard, thecontroller 50 is operable to command the refrigerator 10 to execute thesteps of the method 200 shown in that Figure. To this end, thecontroller 50 determines whether a defrost cycle is necessary at step202. For example, in a time-based defrost cycle, the controller 50 atstep 202 determines whether a predetermined amount of time has elapsedsince the most recent defrost cycle. If so, then the controller 50begins the defrost cycle at step 204. If not, then the controller 50continues to wait and periodically checks to see if the predeterminedamount of time has elapsed. In one example, the refrigerator 10 maydefrost every six hours, in which case the predetermined amount of timewould be six hours. Alternatively, the controller 50 may be operable toperform adaptive defrosts that are spaced by varying amounts of timedepending on operational characteristics measured between defrostcycles, as described in further detail below.

Returning to FIG. 10, when a defrost cycle is required to remove frostbuild up from the evaporator coil 112, the controller 50 stops thecompressor 22 and the evaporator fan 64 at step 204. This stopsrefrigerant flow through the refrigeration fluid circuit 20 and theevaporator 30 and also stops air flow through the evaporator 30. Thecontroller 50 then closes the first and second dampers 66, 68 (or theoutlet valve 132 and the inlet valves 146) at step 206 to thermallyisolate the evaporator compartment 72 from the refrigerated portion 74of the cabinet 12. With the evaporator compartment 72 thermally isolatedfrom the cabinet 12, the controller 50 starts operation of the defrostheater 114 at step 208. The defrost heater 114 warms the evaporator 30and the evaporator coil 112 to melt frost and cause the moisture to driponto the drip pan 116 for removal from the evaporator 30. Theoperational state of the refrigerator 10 at this point is shown in FIG.5. During the operation of the defrost heater 114, the cabinet 12continues to be cooled by the melting of the eutectic plate 122 at step210.

One of the sensors S₃ connected to the evaporator 30 may be configuredto measure the temperature of the evaporator 30. At step 212, thecontroller 50 determines whether that sensor S₃ is reading a temperatureof the evaporator 30 which is at or exceeding a first target temperatureabove the freezing point of water (0° C.). In one example, this firsttarget temperature may be about 10° C. If the evaporator 30 is not at orabove that first target temperature, then the controller 50 continues tooperate the defrost heater 114 to remove frost from the evaporator coil112. If the evaporator 30 is at or above the first target temperature,then the controller 50 turns off the defrost heater 114 and allows a setperiod of time for additional moisture to drip off the evaporator coil112 onto the drip pan 116 at step 214. After this “drip time” hasoccurred, the controller 50 starts the compressor 22 to causerefrigerant flow through the evaporator 30 again at step 216, therebycooling the evaporator compartment 72.

At step 218, the temperature sensor S₃ measures the temperature of theevaporator 30 and the controller 50 determines whether this temperatureis at or below a second target temperature below the freezing point ofwater (0° C.). In one example, this second target temperature may beabout −25° C. If the evaporator 30 is not at or below the second targettemperature, the controller 50 continues to operate the compressor 214to cool the evaporator 30. Once the controller 50 determines that theevaporator 30 is at or below the second target temperature, then thecontroller 50 opens the first and second dampers 66, 68 (or the outletvalve 132 and inlet valves 146) at step 220. The controller 50 alsostarts the evaporator fan 64 at step 220, to thereby force air flow fromthe refrigerated portion 74 through the evaporator compartment 72 andthe evaporator 30 for further cooling. This final step of the defrostcycle or method 200 returns the refrigerator 10 to the operational stateshown in FIG. 6, which is the normal cooling operational state. As aresult of the insulated cover 70 and/or the melting of the eutecticplate 122, the defrost cycle does not cause a significant temperaturespike within the refrigerated interior 18 of the cabinet 12, and therefrigerator 10 therefore is advantageous over conventional refrigeratordesigns.

As briefly noted above, in one alternative embodiment the defrost cyclewill be an adaptive defrost cycle selectively actuated at step 202 ofthe method 200. In this adaptive defrost cycle, the period betweendefrost cycles and the time duration of the defrost cycles are modifiedbased on a plurality of operational parameters monitored by thecontroller 50. For example, the conventional time-based defrost cyclemay operate the defrost heater 114 for 10 minutes every six hours. Bycontrast, the adaptive defrost cycle may monitor the actual temperaturebeing maintained in the cabinet 12, as well as the number of dooropenings and amount of total time the door is open. These and otherfactors are considered to determine how long the period should be beforethe next defrost cycle is started, and also how long the defrost heater114 should be operated in the next defrost cycle. In this regard, if thedoor of the cabinet 12 is not opened often during a six hour period andthe evaporator 30 is having little trouble maintaining the desiredtemperature within the refrigerated portion 74, then the next defrostcycle may be delayed by an additional number of hours and/or shortenedin duration. Thus, the adaptive defrost cycle is highly energy efficientbecause the evaporator coil 112 is only defrosted when that cyclebecomes necessary. Moreover, the adaptive defrost cycle automaticallyadjusts the refrigerator 10 for proper and efficient operation in avariety of environmental conditions.

While the present invention has been illustrated by a description ofexemplary embodiments and while these embodiments have been described inconsiderable detail, it is not the intention of the applicant torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. For example, the air ducts 134, 140 may becombined with the eutectic plates 122 shown in the various embodiments10, 130 of the refrigerator. The invention in its broader aspects istherefore not limited to the specific details, representative apparatusand method, and illustrative example shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of applicant's general inventive concept.

What is claimed is:
 1. A refrigerator, comprising: a cabinet having arefrigerated interior; a refrigeration fluid circuit for circulating arefrigerant, the circuit including a compressor, a condenser, anexpansion device, and an evaporator located within an insulatedevaporator compartment outside the cabinet, and including an evaporatorcoil and an evaporator fan producing air flow through the evaporatorcoil; at least one damper that may open to permit air circulation fromthe refrigerated interior through the evaporator compartment; and aeutectic member configured to melt at an operating temperature of therefrigerator, wherein the evaporator cools the refrigerated interior toa temperature below the operating temperature such that when the atleast one damper is closed for a defrost cycle, the eutectic membercools at least one of the refrigerated interior and the evaporatorcompartment by melting.
 2. The refrigerator of claim 1, wherein thecabinet includes side walls and a top wall, the at least one damper isformed in the top wall, and the eutectic member is mounted along one ofthe side walls.
 3. The refrigerator of claim 1, wherein the eutecticmember is a plate-shaped member.
 4. The refrigerator of claim 1, whereinthe operating temperature is about −32° C.
 5. The refrigerator of claim1, wherein the cabinet includes a top wall, the at least one damper isformed in the top wall, and the eutectic member is mounted along the topwall.
 6. The refrigerator of claim 1, wherein the eutectic member ismounted within the evaporator compartment such that the eutectic membercools the evaporator compartment by melting during a defrost cycle. 7.The refrigerator of claim 1, wherein the cabinet further includes: a topwall adjacent the insulated evaporator compartment, a door, a rear wallincluding an inlet duct in communication with the evaporator and aplurality of inlet ports leading into the refrigerated interior, andside walls extending between the rear wall and the door, each side wallincluding an outlet duct in communication with the evaporator and aplurality of outlet ports leading from the refrigerated interior,wherein the at least one damper is a valve controlling flow between theevaporator and the refrigerated interior via the inlet duct and theoutlet ducts.
 8. A refrigerator, comprising: a cabinet having arefrigerated interior; a refrigeration fluid circuit for circulating arefrigerant, the circuit including a compressor, a condenser, anexpansion device, and an evaporator located within an insulatedevaporator compartment outside the cabinet and including an evaporatorcoil, an evaporator fan producing air flow through the evaporator coil,and a defrost heater; at least one damper that may open to permit aircirculation from the refrigerated interior through the evaporatorcompartment; and a controller operable to command the refrigerator toperform the following steps when the evaporator coil requiresdefrosting: stop operation of the compressor and the evaporator fan;close the at least one damper to thermally isolate the evaporatorcompartment from the refrigerated interior; and start operation of thedefrost heater, wherein the refrigerated interior remains thermallyisolated from the evaporator during operation of the defrost heater. 9.The refrigerator of claim 8, further comprising a temperature sensor fordetecting the temperature of the evaporator, and wherein the controlleris further operable to command the refrigerator to perform the followingsteps during defrosting of the evaporator: when the temperature sensordetects that the evaporator has reached a first target temperature abovethe freezing point of water, stopping operation of the defrost heaterand allowing for any remaining moisture to drip off the evaporator coil;starting the compressor after the remaining moisture drips off theevaporator coil; and when the temperature sensor detects that theevaporator has reached a second target temperature below the freezingpoint of water, opening the at least one damper and starting operationof the evaporator fan.
 10. The refrigerator of claim 9, wherein thefirst target temperature is about 10° C. and the second targettemperature is about −25° C.
 11. The refrigerator of claim 8, whereinthe at least one damper includes a first damper and a second damper, thefirst damper in an open position permitting air flow into the evaporatorcompartment from the refrigerated interior, the second damper in an openposition permitting air flow from the evaporator compartment into therefrigerated interior.
 12. The refrigerator of claim 8, wherein theinsulated evaporator compartment further includes a plurality of vacuuminsulated panels.
 13. The refrigerator of claim 8, further comprising: aeutectic member located within the cabinet and configured to melt at anoperating temperature of the refrigerator, wherein the evaporator coolsthe refrigerated interior to a temperature below the operatingtemperature such that when the at least one damper is closed for adefrost cycle, the eutectic member cools the refrigerated interior bymelting.
 14. The refrigerator of claim 13, wherein the cabinet includesside walls and a top wall, the at least one damper is formed in the topwall, and the eutectic member is mounted along one of the side walls.15. The refrigerator of claim 13, wherein the cabinet includes a topwall, the at least one damper is formed in the top wall, and theeutectic member is mounted along the top wall.
 16. The refrigerator ofclaim 13, wherein the operating temperature is about −30° C.
 17. Therefrigerator of claim 8, further comprising: a eutectic member locatedwithin the evaporator compartment and configured to melt at an operatingtemperature of the refrigerator, wherein the evaporator cools therefrigerated interior to a temperature below the operating temperaturesuch that when the at least one damper is closed for a defrost cycle,the eutectic member cools the evaporator compartment by melting.
 18. Therefrigerator of claim 8, wherein the cabinet further includes: a topwall adjacent the insulated evaporator compartment, a door, a rear wallincluding an inlet duct in communication with the evaporator and aplurality of inlet ports leading into the refrigerated interior, andside walls extending between the rear wall and the door, each side wallincluding an outlet duct in communication with the evaporator and aplurality of outlet ports leading from the refrigerated interior,wherein the at least one damper is a valve controlling flow between theevaporator and the refrigerated interior via the inlet duct and theoutlet ducts.
 19. A method of operating a refrigerator including acabinet having a refrigerated interior, a refrigeration fluid circuitincluding a compressor, a condenser, and an evaporator located within aninsulated evaporator compartment outside the cabinet and having anevaporator fan and defrost heater, the refrigerator further including atleast one damper configured to separate the evaporator compartment fromthe refrigerated interior of the cabinet, and the method comprises:stopping operation of the compressor and the evaporator fan; closing theat least one damper to thermally isolate the evaporator compartment fromthe refrigerated interior; and starting operation of the defrost heater,wherein the refrigerated interior remains thermally isolated from theevaporator during operation of the defrost heater.
 20. The method ofclaim 19, further comprising: when the evaporator has reached a firsttarget temperature above the freezing point of water, stopping operationof the defrost heater and allowing for any remaining moisture to dripoff the evaporator coil; starting operation of the compressor after theremaining moisture drips off the evaporator coil; and when theevaporator has reached a second target temperature below the freezingpoint of water, opening the at least one damper and starting operationof the evaporator fan.
 21. The method of claim 20, wherein the firsttarget temperature is about 10° C. and the second target temperature isabout −25° C.
 22. The method of claim 19, wherein the system furtherincludes a eutectic member located within the cabinet or the evaporatorcompartment and configured to melt at an operating temperature of therefrigerator, and the method further comprises: cooling the refrigeratedinterior with the evaporator to a temperature below the operatingtemperature before a defrost cycle; and melting the eutectic member tocool at least one of the refrigerated interior and the evaporatorcompartment during the defrost cycle.
 23. A refrigerator, comprising: acabinet having a refrigerated interior; a refrigeration fluid circuitfor circulating a refrigerant, the circuit including a compressor, acondenser, an expansion device, and an evaporator located within anevaporator compartment outside the cabinet and including an evaporatorcoil and an evaporator fan producing air flow through the evaporatorcoil; and at least one valve that may open to permit air circulationfrom the refrigerated interior through the evaporator compartment,wherein the cabinet further includes: a top wall adjacent the evaporatorcompartment, a door, a rear wall including an inlet duct incommunication with the evaporator and a plurality of inlet ports leadinginto the refrigerated interior, and side walls extending between therear wall and the door, each side wall including an outlet duct incommunication with the evaporator and a plurality of outlet portsleading from the refrigerated interior, wherein the at least one valvecontrols flow between the evaporator and the refrigerated interior viathe inlet duct and the outlet ducts.
 24. The refrigerator of claim 23,wherein the cabinet includes a bottom wall, and the inlet duct andoutlet ducts each extend between the top wall and the bottom wall.